Nuclear reactors have been used to produce commercially valuable products. For example, isotopes for medical industrial use and plutonium have been produced using nuclear reactors. Specific grades of plutonium have also been produced as well. One such avenue to production of Pu-238 is the nuclear reaction of americium (Am) and/or neptunium (Np) to produce Pu-238.
It is clear that a Pu-238 source is more necessary than ever as in at least one example, Pu-238 can provide the heat source for radioisotope power systems and radioisotope heater units used in NASA space exploration missions and in national security applications. Kilogram-scale production of Pu-238 has not occurred in the United States since 1988, but small quantities of Pu-238 from process demonstrations have been produced at Oak Ridge National Laboratory using the high flux isotope reactor research reactor and theorized at the Idaho National Laboratory using the advanced test reactor research reactor. NASA missions requiring nuclear power have been relying on existing inventories and purchases from Russia, which were suspended in 2009. There are no known sources of Pu-238 outside the U.S. and Russia stockpiles; thus, the total amount available for mission use is fixed. The quantity of Pu-238 that can be produced by research reactors in the United States is limited, constraining the future use of Pu-238 for national security, NASA, and international space agencies. Although the European Space Agency is investigating the use of Am-241 for radioisotope heat and power sources due to its availability in the United Kingdom from aged civilian plutonium stockpiles, Pu-238 is the preferred isotope for space applications.
High-power production reactors have been shut down in the U.S., leaving only the high-power reactors remaining being commercial reactors. Commercial reactors operate at a much higher temperature, and the previous Pu-238 production target designs are not compatible with commercial reactor operating schemes. For example, targets placed in commercial reactors must be able to survive condition 1, 2, and 3 events and not contribute any adverse consequences to the outcome of a condition 4 accident.
As mentioned, past techniques used for producing kilogram quantities of Pu-238 are based on the irradiation of aluminum targets containing neptunium-237 oxide in a nuclear reactor. Post irradiation, aluminum can be dissolved in a caustic bath followed by acid dissolution of the remainder of the target. Following recovery and purification, Pu-238 can be precipitated from a nitrate solution, calcined to an oxide, and processed as a powder into heat source pellets. However, powder processing of Pu-238 oxide is known to create dispersible particles, resulting in gross contamination of glove box equipment, loss to holdup, and significant fractions requiring recycling. In addition to the assemblies provided, a method is also provided that details a sol-gel process for fabricating spheres or microspheres of Np-237 oxide and/or Pu-238 oxide. This allows for the irradiation techniques described herein as well as new and additional irradiation techniques. It reduces contamination during Pu-238 oxide handling and improves Pu-238 oxide processing efficiency, which allows for new Pu-238 oxide heat sources.
The present disclosure provides reactor assemblies, target assemblies, and methods that in certain circumstances can meet the performance metrics that permit use in a commercial reactor. Further, embodiments of the disclosure provide features that can enhance material recovery efficiencies following irradiation, and this may reduce waste volumes compared to prior legacy target assemblies. The present disclosure provides reactor assemblies, reactor target assemblies and methods that can be used to produce Pu-238 from, for example, Am or Np spheres.